PYONGYANG, North Korea - In a bold hacking, North Korea’s cyber army broke into enemy files and is said to have found elaborate plans laid out by U.S. and South Korea to decapitate the North Korean leader, Kim Jong Un.

A lawmaker for South Korea's ruling Democratic Party revealed on Tuesday that a cache of secret U.S.-South Korean military files including plans to take down Kim Jong Un.

The hacking is said to have occurred last year.

According to Rhee Cheol-hee, hackers broke into the Defense Integrated Data Center in September 2016.

Defense ministry officials said that Cheol-hee stole a number of classified documents.

The revelation was first made in April, when a local newspaper, Chosen Ilbo quoted anonymous defense ministry sources as saying that the ministry had previously downplayed the seriousness of the hacking.

Rhee further said that the ministry still has to identify the content of about 80 percent of the 235 gigabytes of data that was stolen.

In a statement quoted in the South Korean news agency Yonhap, the lawmaker said, "The Ministry of National Defense has yet to find out about the content of 182 gigabytes of the total (stolen) data.”

He added that among the stolen files were Operation Plans 5015 and 3100.

Local press reports noted that the operation plans are classified to the point that South Korean lawmakers from both ruling and opposition parties protested about the superficial briefing received by defence officials when they were introduced in 2015.

It was later revealed that OPLAN 5015 also included a pre-emptive strike on the North’s nuclear and missile facilities, as well as “decapitation attacks” against Kim Jong Un and the rest of the North Korean leadership.

Rhee said that the hackers have also gained information about state-of-the-art military facilities, power plants and the joint military drills with the U.S. as well as reports meant for U.S. commanders.

Soon after reports emerged, North Korea denied any role in the hacking.

However, the reclusive nation boasts of a group of elite hackers, who have honed their skills over the years and have led massive hack attacks across the world.